The invention relates to an arrangement for profiling a fibre web on a shoe roll.
In shoe calenders, the nip pressure is usually in the range from 2–15 Mpa and the nip pressure is controlled by means of the tilt of the shoe element combined with loading. A shoe calender has a relatively long shoe element in the machine direction, often of up to 270 mm or more, thus allowing good surface smoothness of the fibre web while preserving the bulk, because despite the relatively high loading pressure of the shoe element, the maximum pressure in the roll nip will remain relatively low.
However, especially in pre-calendering of the fibre web, surface thickness profiling is often required in addition to surface smoothness profiling of the fibre web. Current shoe calenders are not suitable for surface thickness profiling, because the maximum compression load achieved in the roll nip with these is relatively low despite the high loading pressure of the shoe element. If a shoe calender is used for pre-calendering a fibre web such as a cardboard web, one has nowadays to carry out thickness profiling of the fibre web surface with a separate hard profiling roll. A separate calender for thickness profiling increases the machine direction space requirement regarding the shoe calender alone, and also increases the purchasing and operating costs of the paper and cardboard making machine. If a hard roll for surface thickness profiling is brought into contact with the counter-roll of the shoe roll (thermo-roll), the machine direction space requirement will decrease, but the operating and purchasing costs of the installation are still higher than they would be, could a shoe calender alone be used for pre-calendering. In some cases, the fibre web feed may also cause problems.
The arrangement of the invention and the shoe roll used in it are intended to overcome the shortcomings in the prior art.